1. Field of the Invention
The present invention relates to a filter for aluminum hot melt which filtrates solid impurities contained in aluminum hot melt. More particularly, the present invention relates to a ceramic filter and an improvement of an inorganic binder which is used for binding aggregate particles.
2. Description of the Related Art
Aluminum sheet or foil has previously been produced by rolling an ingot into which aluminum hot melt is cast. If the ingot is contaminated by solid impurities, such as minute fragments of metal oxides or refractories contained in the aluminum hot melt, pinholes or surface defects may arise in the sheet or foil during the rolling of the ingot when manufacturing such products. The prevention of these defects requires the removal of the solid impurities contained in the hot melt. Accordingly, conventional means, for example, a porous ceramic cylindrical filter, have been used. This filter for aluminum hot melt has been produced in such a way that aggregate particles of such materials as silicon carbide, silicon nitride, and alumina are mixed up with inorganic binding raw material, and the resulting material is formed into a cylindrical shape, heated to a predetermined temperature, and subsequently cooled. Such a production method provides a porous ceramic having numerous minute consecutive pores formed between aggregate particles which are bound to each other by a vitreous inorganic binder.
In such a porous ceramic, silica-based glass is employed as an inorganic binder which binds aggregate particles. Accordingly, SiO.sub.2 contained in the inorganic binder reacts with the aluminum hot melt to generate free silicon which will contaminate the hot melt. This resulting contamination of the aluminum hot melt causes cracking and other defects during the rolling of an aluminum ingot. Such contamination means that the aluminum hot melt will erode the inorganic binder. Therefore, after long term use, the strength of the filter decreases, with the result that the life thereof is shortened.